Power bus voltage drop compensation using sampled bus resistance determination

ABSTRACT

A power system includes a power conversion stage that receives power from an input source and delivers power to a load via a power distribution bus. The power distribution bus may include a DC transformer such as a fixed ratio bus converter or VTM having an equivalent series resistance. A control system samples the voltage delivered by the power conversion stage at a location close to the output of the power conversion stage, and the load voltage at a location close to the load. The samples may be synchronized by means of a data bus that provides communication between a control device and an output monitor. Synchronization may be accomplished within a sampling period that is short relative to changes in the voltages and currents. Each set of samples may be used to determine a value of the bus resistance. Multiple samples may be averaged to improve accuracy in the determination. The determined bus resistance, including the equivalent series resistance of any bus converter, may be used to introduce a negative resistance characteristic in the power conversion stage as a way of compensating for the actual bus resistance without resorting to full bandwidth feedback from the load.

TECHNICAL FIELD

This invention relates to apparatus and methods for compensating for voltage errors introduced by a non-ideal power distribution connections between a power converter and a load.

BACKGROUND

Non-ideal connections between the output of a power converter and its load may introduce a voltage drop which may vary as a function of changes in load current owing to the resistance in the non-ideal connection. Traditional attempts to compensate for such errors include using negative feedback to compare the voltage at the load to a desired reference voltage requiring relatively high bandwidth connections between the load and the power converter due to the need to constantly monitor and control the voltage at the load. Other attempts have accounted for resistances in the system by providing a correction circuitry based on an expected resistance in the line. Thus, it would be advantageous to have systems and methods that provide for maintaining a voltage at a load, and accounting for variations in bus resistance over time, while reducing the bandwidth required to maintain a desired load voltage.

SUMMARY

One exemplary method of the present disclosure is a method of converting power. The method includes providing a first power conversion stage. The first power conversion stage including an input for receiving power from a power source and a first output for supplying power via a first power bus to a first load. The first load is electrically separated from the first output by a first bus resistance. The method further includes providing a control circuit adapted to provide a control signal to the first power conversion stage. The method further includes measuring a first load voltage at or near the first load, measuring a first output voltage at or near the first output, and measuring a first current flowing between the first output and the first load through the first power bus. The method additionally includes determining a representation of the first bus resistance as a function of the measuring using the control circuit. The method also includes sending a control signal to the first power conversion stage from the control circuit as a function of the representation of the first bus resistance. Furthermore, the method includes adjusting, in response to the control signal, the first power conversion stage to include a negative output resistance component configured to compensate for the first bus resistance.

Another exemplary embodiment of the present disclosure is a method of converting power. The method includes providing a plurality of power conversion stages each having a respective input for receiving power from a power source and a respective output for supplying power via a respective power bus to a respective load, each load being electrically separated from the respective output by a respective bus resistance. The method further includes providing a control circuit adapted to provide a respective control signal to the each of the plurality of power conversion stages. The method further includes measuring a respective load voltage of the power being supplied to each load at or near the load, and measuring a respective output voltage being supplied to each load at or near the respective output. The method further includes determining a representation of the respective bus resistance as a function of the respective measuring. The method also includes sensing a respective control signal to each power conversion stage as a function of the representation of the respective bus resistance. The method also includes adjusting, in response to a respective control signal, a response characteristic of each power conversion stage to include a negative output resistance component configured to compensate for the respective bus resistance.

Another exemplary embodiment of the present disclosure is a system of converting power. The system includes a first power conversion stage. The first power conversion stage includes an input for receiving power from a power source, and a first output for supplying power via a first power bus to a first load, the first load being electrically separated from the first output by a first bus resistance. The system further includes a control circuit. The control circuit is adapted to measure a first output voltage at or near the first output and a first current flowing between the first output and the first load through the first power bus. The system also includes an output monitor, the output monitor configured to measure a first load voltage at or near the first load. In the system, the control circuit is configured to determine a representation of the first bus resistance as a function of the measuring using the control circuit, and additionally configured to send a control signal to the first power conversion stage from the control circuit as a function of the representation of the first bus resistance. The first power conversion stage is configured to adjust a voltage at the first output to include a negative output resistance component to compensate for the first bus resistance in response to the first control signal.

DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a power delivery system according to one embodiment.

FIG. 1B shows the power delivery system of FIG. 1A, including a DC transformer, according to one embodiment.

FIG. 2 shows a relationship between current and voltage in the systems of FIG. 1A.

FIG. 3A illustrates sample timing in one embodiment of a power delivery system according to one embodiment. FIG. 3B illustrates an expanded view of the sample timing of FIG. 3A.

FIG. 4 shows another power delivery system according to one embodiment.

DETAILED DESCRIPTION

Electronic systems may comprise one or more power sources (e.g. voltage regulators) that deliver power to one or more loads by means of one or more power distribution buses. A power distribution bus may comprise, e.g., cables, bus bars, printed circuit board traces and other conductive devices. Because the power distribution bus has finite resistance there will be a voltage drop in the bus that will vary as a function of load current. In some systems the effects of bus resistance may be minimized by providing distribution bus conductors of sufficiently large gauge to keep the maximum voltage drop in the bus below some desired maximum value. This, however, may result in a distribution bus that is bulky, heavy and costly. Another way to reduce the effects of distribution bus voltage drop is to control the voltage output of the power source as a function of the voltage measured at the load, thereby reducing or eliminating errors in voltage, e.g. due to voltage drop in bus as a function of load current. This approach has required using wideband feedback from the load, with associated additional interconnection, processing bandwidth, stability, and control issues.

A first embodiment of a power distribution system 10A is shown in FIG. 1A having a power delivery stage 15A (comprising a power conversion stage 30 and a power distribution bus 40) connected to supply power to a load 50. The power conversion stage 30 receives power from an input source 20 and delivers power, at an output voltage V_(O) and an output current I_(O), to load 50 via a distribution bus 40. The total resistance, R_(B), in the distribution bus is indicated in FIG. 1A by lumped bus resistances 42, 44. A power conversion controller 32 in the power conversion stage 30 may control the magnitude of the output voltage, V_(O) by supplying a control signal to a voltage regulator 34 within the power conversion stage 30. The control bandwidth, BW, of the power conversion controller 32 may be sufficiently large to enable the voltage V_(O) to be maintained within pre-defined limits (e.g. 0.1%, 1%) under normal operating conditions, e.g. at the maximum slew rate and variation in magnitude of the output current, I_(O), demanded by the load 50.

A control circuit 70 may be provided to measure the output voltage, V_(O), and optionally the output current, I_(O), and to deliver a control signal 90 to the power conversion stage 30. The control circuit 70 may be configured as a function in a larger supervisory system for managing operation, e.g. power up, fault detection, and power down, of the power conversion stage 30, or as a dedicated auxiliary circuit. An output monitor 60 may be provided to measure the load voltage V_(L) and optionally the output current, I_(O), and communicate with the control circuit 70. The output monitor 60 may be similarly deployed as a function of a larger monitoring circuit, such as a supervisory load monitoring circuit, or as a dedicated auxiliary circuit. Data and control signals may pass between the control circuit 70 and the output monitor 60 via data bus 80, which may be of any form (e.g. analog, digital, physical conductors, wireless), and use any form of communication protocol (e.g. PMBus, I2C, etc.).

Bus resistance, R_(B), causes a reduction in the load voltage, V_(L), relative to the output voltage as a function of output current, V_(O): V_(L)=V_(O)−I_(O)*R_(B). A method for counteracting the effect of the bus voltage drop, I_(O)*R_(B), comprises using the control circuit 70 to make measurements of the output voltage V_(O), and using the output monitor 60 to make a measurement of the load voltage V_(L), and using one or both of the control circuit 70 or output monitor 60 to measure the output current I_(O). The measurements made by the output monitor 60, e.g. of V_(L) and optionally I_(O), may be provided to the control circuit via data bus 80. The control circuit 70 may use the measured values of V_(O), I_(O) and V_(L) to determine a magnitude of bus resistance: R_(BD)=(V_(OM)−V_(LM))/I_(OM), where R_(BD) is the determined magnitude of the bus resistance, and V_(OM), V_(LM) and I_(OM) are the respective measured values of V_(O), V_(L) and I_(O). R_(BD) may be delivered to the power conversion circuit 30, by means of control signal 90, where it may be used to alter the magnitude of V_(O)(t) as a function of the magnitude of the load current I_(O). If, for example, it is desired to maintain the load voltage at an essentially constant voltage V_(L)=V_(LD), the power conversion circuit would set V_(O)=V_(LD)+R_(BD)*I_(O), where V_(LD) is the desired load voltage. In this way, V_(O) will be controlled to offset and compensate for the voltage drop in the power bus, I_(O)*R_(B), thereby reducing or eliminating variations in V_(L).

The relationship between V_(O) and I_(O) is shown in FIG. 2. Because V_(O) increases with increasing I_(O), the power conversion stage 30 exhibits a negative output resistance characteristic that counteracts and compensates for the effects of the finite, positive, bus resistance.

The accuracy of the determined value of resistance, R_(BD), will be affected by the relative timing (synchronization error) of the measurements of V_(O), V_(L) and I_(O). Accuracy is improved if all of the measurements are made within a sampling time period during which the values of V_(O), V_(L) and I_(O) do not vary significantly. The method may therefore comprise synchronizing the measurements of V_(O), V_(L) and I_(O) to occur within a sampling period, T_(S), that is short with respect to anticipated changes in V_(O), V_(L) and I_(O). By this we mean that T_(S) is short enough so that anticipated variations in average values of V_(O), V_(L) and I_(O) do not exceed a small percentage (e.g., 0.1%, 1%) of their values at the beginning of the sampling period. For example, the sampling period may be a very small fraction of a second, e.g. 1 mS, 100 uS, 10 uS, 1 uS, 100 nS, 10 nS, etc. The control circuit 70 may synchronize the taking of the measurements by sending a synchronization signal to the output monitor 60, via data bus 80. Within a very short time after receiving the synchronization signal the output monitor 60 takes a sample of the load voltage, V_(LM). Also within a very short time period of sending the synchronization signal, the control circuit 70 takes samples of output voltage, V_(OM), and preferably the output current, I_(OM). In this way, sampled measurements of V_(OM), V_(LM) and I_(OM) may be synchronized to all be taken at some time, and preferably at the same time, within the short sampling period T_(S).

Effects associated with timing of samples and transient load changes may introduce errors into individual determined values of R_(BD). The method may therefore incorporate an averaging process to improve accuracy in the determination of R_(BD). For example, as illustrated in FIG. 3A, an averaging interval, T_(D), may comprise a finite number, N, of sequential sample intervals of length T_(S). The averaging interval may preferably be made long relative to any synchronization errors in the samples. For example, a system may use 100 uS sampling intervals, T_(S), and obtain 100 contiguous samples per 10 mS averaging interval, T_(D). As shown in FIG. 3B, which shows an expanded view of a portion of FIG. 3A, samples of V_(O), V_(L) and I_(O) are taken within each sampling interval. The durations of both the sampling period, T_(S), and the averaging interval, T_(D), are made short with respect to anticipated changes in the average values of V_(O), V_(L) and I_(O). The N values of R_(BD) that are determined during the averaging interval, T_(D), are averaged by control circuit 70 to provide an averaged determined value, R_(BDA). R_(BDA) is delivered to the power conversion circuit 30 where it is used, in the manner discussed earlier, to change the magnitude of V_(O) as a function of the magnitude of the load current I_(O): V_(O)=V_(LA) R_(BDA)*I_(O). Although sampling periods are shown to be contiguous in FIG. 3A, it is understood that sampling intervals may be separated in time within an averaging interval. Any suitable method of averaging the values may be used. For example, a simple mathematical average of all of the data points may be used to calculate the averaged determined value; alternatively the data points may be screened to eliminate any that differ by more than a predetermined percentage, such as 10% or 5% or less, from the other data points.

Although the bus resistance may change over time, e.g. due to temperature changes or other environmental effects, the changes should occur very slowly compared to V_(O), V_(L), and I_(O) for typical electronic loads. The frequency with which the bus resistance or average bus resistance is determined and delivered to power conversion circuit 30 may therefore be low compared to the control bandwidth, BW, of the power conversion controller 32. Accordingly a single supervisory circuit or controller may be used to service a plurality of conversion circuits and loads.

A second embodiment of a power distribution system 10B is shown in FIG. 1B, having a power delivery stage 15B. The power delivery system 15B may be the same as power delivery system 15A, but further includes a DC transformer 43, such as a fixed-ratio bus converter, or voltage transformation module (“VTM”), in the power path between the regulator 34 and the load 50 to implement various power distribution architectures, as described below. Accordingly, operation of the system 10B in FIG. 1B is substantially the same as that of system 10A of FIG. 1A, except as described below. For example, power distribution architectures such as those described in Vinciarelli, Factorized Power Architecture with Point of Load Sine Amplitude Converters, U.S. Pat. No. 6,984,965, issued Jan. 10, 2006 (the “FPA Patent”), and in Vinciarelli et al., Power Distribution Architecture with Series-Connected Bus Converter, U.S. application Ser. No. 13/933,252 filed Jul. 2, 2013 (the “NIBA Application”), both of which are assigned to VLT, Inc., and are herein incorporated by reference, in their entirety may be implemented.

As defined herein, the DC transformer 43 delivers a DC output voltage, V_(OUT), which is a fixed fraction of the input voltage, V_(IN), delivered to its input. The DC transformer 43 may also provide isolation between an input of the DC transformer 43 and an output of the DC transformer 43. The voltage transformation ratio and/or voltage gain of the DC-transformer 43 is defined herein as the ratio of the output voltage to the input voltage at a load current. Expressed mathematically, the voltage transformation ratio and/or voltage gain may be expressed as K=V_(OUT)/V_(IN). The voltage transformation ratio of a DC transformer, such as DC transformer 43, may be fixed by design, e.g. by a converter topology, timing architecture, and/or the turns ratio of the transformer.

In one embodiment, the DC transformer 43 may be implemented using Sine-Amplitude Converter (“SAC”) topologies and/or timing architectures, such as those described in Vinciarelli, Factorized Power Architecture and Point of Load Sine Amplitude Converters, U.S. Pat. No. 6,930,893, and in Vinciarelli, Point of Load Sine Amplitude Converters and Methods, U.S. Pat. No. 7,145,786, both assigned to VLT, Inc., and incorporated herein by reference in their entirety (hereinafter the “SAC Patents”), as well as those described in the NIBA Application, discussed above. The DC transformer 43, using a SAC topology, may be capable of achieving very high power densities and conversions efficiencies for voltage transformation at an essentially resistive output resistance. The SAC topology may also provide galvanic isolation between an input of the DC transformer 43 and an output of the DC transformer 43, with an equivalent output resistance. To the extent the DC transformer 43 is essentially resistive and experiences voltage droop with increases in current, the sampled bus compensation system may be used to correct for the equivalent series resistance 45 of the DC transformer 43 in addition to the lumped bus resistances 42-1, 42-2, 44-1, 44-2, of the bus segments 40-1, 40-2. As described in the '965 Patent and the '252 Application, the DC transformer 43 may provide voltage reduction and current multiplication. In one embodiment, the voltage gain may be less than one (K<1), or more preferably, (K≦¼). Further, the DC transformer may be located relatively closer to the load 50, than to the regulator 34, thereby allowing the output voltage, V_(O), of the regulator 34 to be greater than the load voltage, V_(L). In one embodiment, the output voltage, V_(O), is greater than the load voltage, V_(L), by a factor of four or more.

FIG. 4 shows an embodiment of a power distribution system 100 having a plurality of power delivery stages, 15 ₁, 15 ₂, each of the kind shown in FIG. 1A and each comprising an input source 20 ₁, 20 ₂, a power conversion stage 30 ₁, 30 ₂, a distribution bus 40 ₁, 40 ₂ and a load 50 ₁, 50 ₂. The input voltages, Vin1 and Vin2, may come from different sources 20 ₁, 20 ₂, or the input voltages Vin1 and Vin2 may come from the same source. The total resistance in each distribution bus 40 ₁, 40 ₂ is indicated in FIG. 4 by lumped bus resistances 42 ₁, 44 ₁ and 42 ₂, 44 ₂. Operation of the system of FIG. 4 is substantially the same as that of the system 10A of FIG. 1A, except that the system of FIG. 4 uses a single control circuit 70 ₁, a single output monitor 60 ₁ and a single data bus 80 ₁ to determine bus resistances, and optionally averaged bus resistances, for the multiplicity of power delivery stages 15 ₁, 15 ₂, and communicate those resistances to the respective power conversion stages 30 ₁, 30 ₂ as control signals 90 ₁, 90 ₂. Although the system of FIG. 4 shows two power delivery stages 15 ₁, 15 ₂, it will be evident that any number of power delivery stages can be operated in accordance with the methods described herein. Furthermore, a single control circuit 70 ₁ can be used to provide a control signal to several (e.g. 3, 5, 12, etc.) power conversion stages and a single output monitor 60 ₁ can be used to sample and communicate data from several loads (e.g. 4, 7, 11). The numbers of control circuits and output monitors may be different, depending on performance capabilities and requirements, and the number of data buses required will depend on the nature of the selected communication technique. The sampled bus compensation system described above may provide superior performance compared to other techniques because it may be used to compensate for the initial value tolerance, variability in time and temperature dependency of all resistive elements in the power path.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, essentially complete cancellation of bus resistance may not be required in all systems; in such systems the magnitude of R_(BD) may be scaled appropriately. 

What is claimed is:
 1. A method of converting power comprising: providing a first power conversion stage including an input for receiving power from a power source and a first output for supplying power via a first power bus to a first load, the first load being electrically separated from the first output by a first bus resistance; providing a control circuit adapted to provide a control signal to the first power conversion stage; measuring a first load voltage at or near the first load; measuring a first output voltage at or near the first output; measuring a first current flowing between the first output and the first load through the first power bus; determining a representation of the first bus resistance as a function of the measuring using the control circuit; sending a control signal to the first power conversion stage from the control circuit as a function of the representation of the first bus resistance; adjusting, in response to the control signal, the first power conversion stage to include a negative output resistance component configured to compensate for the first bus resistance.
 2. The method of claim 1, further comprising synchronizing the measuring steps.
 3. The method of claim 2 wherein the synchronizing comprises performing the measuring steps serially within a time period that is short relative to changes in the first current.
 4. The method of claim 2, further comprising: performing the measuring steps repeatedly over a time interval that is small relative to changes in the first current or the first output voltage; and wherein the determining comprises determining an average representation of the first bus resistance.
 5. The method of claim 1 wherein the providing the control circuit further comprises: providing an output voltage monitor adapted to sample the first output voltage and communicate with the control circuit; and providing a first load monitor adapted to sample the first load voltage and communicate with the control circuit.
 6. The method of claim 1 further comprising: providing a second power conversion stage including an input for receiving power from the power source and a second output for supplying power via a second power bus to a second load, the second load being electrically separated from the second output by a second bus resistance; measuring a second load voltage at or near the second load; measuring a second output voltage at or near the second output; measuring a second current flowing between the second output and the second load through the second power bus; determining a representation of the second bus resistance as a function of the measuring; sending a control signal to the second power conversion stage as a function of the representation of the second bus resistance; and adjusting, in response to the control signal, the second power conversion stage to include a negative output resistance component configured to compensate for the second bus resistance.
 7. The method of claim 6 wherein the providing the control circuit further comprises: providing an output voltage monitor adapted to measure the first output voltage, measure the second output voltage, and communicate with the control circuit; and providing a load monitor adapted to measure the first load voltage, measure the second load voltage, and communicate with the control circuit.
 8. The method of claim 6 further comprising synchronizing the measuring steps.
 9. The method of claim 8 wherein the synchronizing comprises performing the measuring steps serially within a sample period that is short relative to changes in the first current, the second current, the first output voltage, or the second output voltage.
 10. The method of claim 9, further comprising: performing the measuring steps repeatedly over an averaging interval that is long compared to the sample period and short relative to changes in the first current, the second current, the first output voltage, or the second output voltage; and wherein the determining comprises determining an average representation of the first bus resistance and the second bus resistance.
 11. The method of claim 1, further comprising: providing a DC transformer power conversion stage including an input for receiving power from the first output, an output for supplying power to the first load, a fixed voltage transformation ratio, K=VO/VIN, and an equivalent series impedance, the equivalent series impedance including an equivalent series resistance, wherein the first bus resistance includes the equivalent series resistance.
 12. The method of claim 11, wherein K is less than
 1. 13. The method of claim 11, wherein K is less than ¼.
 14. A method of converting power comprising: providing a plurality of power conversion stages each having a respective input for receiving power from a power source and a respective output for supplying power via a respective power bus to a respective load, each load being electrically separated from the respective output by a respective bus resistance; providing a control circuit adapted to provide a respective control signal to the each of the plurality of power conversion stages; measuring a respective load voltage of the power being supplied to each load at or near the load; measuring a respective output voltage being supplied to each load at or near the respective output; determining a representation of the respective bus resistance as a function of the respective measuring; sending a respective control signal to each power conversion stage as a function of the representation of the respective bus resistance; and adjusting, in response to a respective control signal, a response characteristic of each power conversion stage to include a negative output resistance component configured to compensate for the respective bus resistance.
 15. The method of claim 14, further comprising synchronizing the measuring steps.
 16. The method of claim 15, wherein the synchronizing comprises performing the measuring steps serially within a predetermined sample period.
 17. The method of claim 15, further comprising: performing the measuring steps repeatedly over an averaging interval, the averaging interval equal to a predetermined number of sampling periods; and wherein the determining comprises determining an average representation of the first bus resistance.
 18. A system of converting power, the system comprising: a first power conversion stage, the first power conversion stage comprising: an input for receiving power from a power source; and a first output for supplying power via a first power bus to a first load, the first load being electrically separated from the first output by a first bus resistance; a control circuit, the control circuit adapted to provide a first control signal to the first power conversion stage, and further adapted to measure a first output voltage at or near the first output, and a first current flowing between the first output and the first load through the first power bus; an output monitor, the output monitor configured to measure a first load voltage at or near the first load; wherein the control circuit is further configured to determine a representation of the first bus resistance as a function of the measuring using the control circuit; and additionally configured to send a control signal to the first power conversion stage from the control circuit as a function of the representation of the first bus resistance; and wherein the first power conversion stage is configured to adjust a voltage at the first output to include a negative output resistance component to compensate for the first bus resistance in response to the first control signal.
 19. The system of claim 15, wherein the control circuit is further configured to synchronize the measurement of the first load voltage, the first output voltage and the first current.
 20. The system of claim 15, further comprising: a second power conversion stage, the second power conversion stage comprising: an input for receiving power from a power source; and a second output for supplying power via a second power bus to a second load, the second load being electrically separated from the second output by a second bus resistance; wherein the control circuit is further adapted to provide a second control signal to the second power conversion stage, and further adapted to measure a second output voltage at or near the second output, and a second current flowing between the second output and the second load through the second power bus; wherein the output monitor is configured to measure a second load voltage at or near the second load; wherein the control circuit is further configured to determine a representation of the second bus resistance as a function of the measuring using the control circuit; and additionally configured to send a control signal to the second power conversion stage from the control circuit as a function of the representation of the second bus resistance; and wherein the second power conversion stage is configured to adjust a voltage at the second output to include a negative output resistance component to compensate for the second bus resistance in response to the second control signal. 